Manually operated small lubricators, commonly referred to as "grease guns", have found considerable success in the past several decades in the private consumer market frequently for personal automobile lubrication. These lubricators usually include a cylinder with one closed end that acts as a reservoir for grease which is loaded into the cylinder in several ways, one being with a prefilled cartridge, another by bulk loading lubricant directly into the cylinder and a third being by pressure loading the cylinder. The cylinder has an open end that is closed by a dispensing head that has a piston reciprocably mounted therein that forces lubricant under pressure through an outlet fitting usually extending forwardly from the head. The highly viscous lubricant is urged forwardly in the cylinder toward the head by the continuous force of a spring biased follower assembly in the rear of the cylinder that frequently includes an elastomeric follower that actually is a piston having a diameter equal to or somewhat larger than the inside diameter of the cylinder.
The dispensing piston is reciprocated in the head by a lever, frequently constructed of sheet metal, that is pivotally connected to the head by a sheet metal link and also pivotally connected to an end of the piston that projects from the head. The link is necessary to accommodate the crank-like movement of the lever as it reciprocates the piston linearly. The link is usually fastened to both the head and the end of the lever by rivets and the piston is connected to the lever in the same manner.
The head itself is usually constructed of metal and requires machining after casting of the outlet fitting, the cylinder receiving portion, the inlet and outlet passages as well as the main bore in the head that slidably receives the piston.
Frequently grease fittings against which the grease gun outlet fitting is impressed to supply lubricant become clogged with foreign material and considerable grease pressure is required to break up this foreign material and deliver lubricant through the fitting. In such cases it is desirable to have a short effective lever arm acting on the piston to achieve high pressure without particular regard for the volume of lubricant being dispensed. Conversely, in cases where the fittings are clear, lubricant pressure is not as important as the volumetric discharge capacity and in this case it is desirable that the effective lever arm acting on the piston be fairly long to dispense lubricant more rapidly.
One attempt to incorporate both functions in a single lever gun, is a dual pressure lever gun models 1013 and 1145, manufactured by Lincoln Engineering. This lever gun incorporates a two-position pivot that varies the effective length of the crank arm between the forward link and the sliding piston. This enables the lever gun to achieve either a long stroke mode or a short stroke mode to accomplish respectively either high volume (low pressure) or high pressure (low volume) delivery. In order to shift the lever from long stroke to short stroke it is necessary to remove a pivot pin connection between the forward link and the lever and replace it in another position on the lever. This is a rather time-consuming process and therefore discourages the operator from shifting from one mode to the other, and this of course detracts from the purpose and effectiveness of the dual mode function.
It is a primary object of the present invention to ameliorate the problems noted above in hand operated lever grease guns.